EW YORK — Roger Federer already has dropped two more sets at the U.S. Open than he did during his entire two weeks en route to the title at Wimbledon. Worried about a recent back problem that kept him from getting

Studies show that physical activity in childhood can psoitively affect the developing brain. Photograph: YakobchukOlena/Getty Images/iStockphoto Last week, Public Health England said 6 million middle-aged adults in England take less than 10 minutes’ brisk exercise a month, risking their health. But when does